Schmelz made two appearances in the major leagues. His first came on September 7
, 1967 - the 23-year-old rookie pitched against the St. Louis Cardinals in relief of Jerry Hinsley. He threw two innings and allowed one run of three hits and a walk. He also struck out two batters, including future Hall of Famer Orlando Cepeda.

His next, and final, appearance came on September 24. He came into the game to relieve Don Cardwell and, despite giving up a hit, left the game without surrendering a run.

Schmelz pitched in the minor leagues from 1966 to 1969 in the Mets' (1966-1969), Oakland Athletics (1968) and Pittsburgh Pirates (1969) systems. Overall, he went 29-36 with a 3.13 ERA in 93 games (91 starts).

He showed flashes of excellence at times throughout his career. For example, in his first professional season, he went 15-5 with a 2.97 ERA for the Auburn Mets and Williamsport Mets. The following year, he posted a 2.60 ERA for Williamsport.